When water warms in summer, it’s essential to take extra care when handling fish. Science explains why

It is rare to see the water temperature on Lake of the Woods touch the 80°F (27°C) mark, but that is where it was the other day when we headed the Kingfisher down lake. There was ice on the one million acre body of water only 15 weeks ago, and now it feels like a bubble bath. How quickly conditions change in the north-country.

But what does it mean for big predators like muskies? And more to the point, should we lay off fishing for them until the water temperature cools? That was just one of the many questions we had for Dr. Sean Landsman, when we interviewed the Carlton University instructor recently on our Doc Talks Fishing Podcast.

“It’s probably safe to say that musky activity is going to peak in the 70°F to 75°F range,” says Landsman, who penned Project Noble Beast, a modern muskie masterpiece. “That relates to what we know about their preferred temperatures. There was [research] from one of the big cooling reservoirs down south for a nuclear power plant, where the muskies had really hot temperatures they could access. And they had really cold temperatures down at the bottom they could access.  They chose somewhere in between.

“Anglers that fish the south will tell you that when it gets really hot, the fishing gets really bad. And that was one of the conclusions that came out of the warm-water mortality studies. There’s a small percentage of that overall population that’s still vulnerable to angling, but above a certain temperature the fish have to work so hard to just maintain their bodies that their activity levels get really low.”

Most muskie anglers have settled on the 80°F mark as that upper stress level temperature, but in large bodies of water that stratify, like Lake of the Woods, Eagle Lake, Lac Seul, Georgian Bay and Lake Nipissing is it as traumatic?

“There were three warm-water mortality studies that were done in the south, in response to the work that we did up here for Project Noble Beast,” says Landsman. “We demonstrated that there’s negligible mortality. We didn’t find any fish that we tagged die. And so our conclusion is that based on current handling practices, mortality is very likely very low. Now, the caveat to that is we didn’t tag fish above 26° (78.8 °F) Celsius. So that’s just shy of 80°F.

“I think it’s fair to say, we can boil it down to this: above 76°F to 77°F, but certainly above 80°F, the risk of mortality increases. The caveat is that those estimates were generated when the fish were treated the way you would normally treat a fish at 65 °F.  You cannot expect to get the same kind of outcome from a fish caught in 83°F water as in 65° F water, if you’re handling it the same.

“The worst thing we can do to a fish is take it out of the water. Period. Hard stop. So if you’re holding the fish out of the water and treating it exactly the same at 80°F, as you do at less than 75°F, you can’t expect to get the same kind of outcomes.”

According to Landsman, muskie anglers have a responsibility to behave  differently when surface water temperatures rise into the high 70s Fahrenheit or mid-20s Celsius. And that starts with never taking the fish out of the water.

“The bump boards we use all float,” he says, “so put it in the water and get the in-water measurement. The other thing that I will do is push the fish’s head down so that it’s accessing colder water. It’s may be not a ton colder, but it should be a little cooler, and the cooler water will hold more oxygen. The other thing I would say, too, and this goes for all water temperatures, when you let the fish go, just let it go. You don’t need to sit there and splash it back and forth.

Concluding his thoughts on the hot water subject, Landsman related that most of the American studies were conducted on small, shallow, southern bodies of water that lack the cold water refugias offered in most Canadian lakes, so we have a distinct advantage.

“In a place like Lake of the Woods, that’s huge and stratifies,” he says, “or has plenty of cold water habitat, even if you have the odd week long period during the summer where water temperatures are hovering in the low 80s at the surface, there’s going to be cold water for them.  And our bio-logger data that we’re collecting on the Rideau River seems to indicate that the fish go down to the bottom even if you’re in eight feet of water or there’s 10-, 12- or 15-feet close by. That fish is going to go down and find colder water and hang out there for a while. What our final bio-logger data seems to be showing is that they hang out a few hours and then they’re back to normal.”

To listen to the entire fascinating podcast with Sean Landsman, that covered a wide range of muskie topics, check out Doc Talks Fishing on your favourite podcast provider or just click on the link below. Enjoy!